Getting a shot of the COVID-19 vaccine during pregnancy works to pass on protection against the virus to newborns during their most vulnerable early months of life, a new study published by the Centers for Disease Control and Prevention reported.

Maternal vaccination was 54% effective against COVID-19 hospitalization in infants younger than 3 months old over the past season. 

The findings from the CDC-backed Overcoming COVID-19 Network were published Thursday in the agency’s Morbidity and Mortality Weekly Report. They drew from data on hospitalizations from 26 pediatric hospitals around the country through May 2023.

The effectiveness dropped to 35% when measured in infants from 3 to 5 months old.

COVID vaccines are currently approved in the U.S. for children ages 6 months and up, but not the youngest babies. So “these findings indicate that maternal vaccination during pregnancy could help prevent COVID-19–related hospitalization in infants too young to be vaccinated,” the study’s authors wrote. 

Protection for both mother and baby

The findings are far from the first to find benefits from vaccination during pregnancy. 

Previous results from the Overcoming COVID-19 Network, earlier during the pandemic, also found vaccine effectiveness up to 80% in babies born to moms who had timed getting their shots later during their pregnancy. 

The American College of Obstetricians and Gynecologists have also urged eligible pregnant parents to get vaccinated. They point to numerous studies showing the shots are safe and can blunt the risk of severe illness for expectant parents as well.

Pregnancy can raise the risk of severe COVID-19. Catching the virus during pregnancy can also pose an increased risk of complications, including stillbirth, though the CDC says the “overall risks are low.”

The CDC’s new findings come as babies now rank as one of the age groups seeing the worst hospitalization rates from COVID-19.

“Hospitalization rates have increased in all age groups since mid July. Hospitalization rates remain highest in older adults and in young infants, less than six months of age,” the CDC’s Dr. Fiona Havers told a panel of the agency’s outside vaccine experts earlier this month.

Havers was presenting data from the agency’s COVID-NET system, which also found rates of hospitalizations remained worse in babies from COVID-19 than they were for influenza.

“Most children under 5, hospitalized with COVID-19 illness, have no underlying medical conditions,” she said.

How does maternal immunization for COVID-19 work?

The ability of maternal immunization to offer protection to babies has been well studied. 

Pregnant moms have long been recommended to get shots to protect babies from other  diseases like pertussis, also known as whooping cough, so they can pass on antibodies to their baby during pregnancy.

A new vaccine for RSV, or respiratory syncytial virus, is also now recommended for use this fall during pregnancy as an option to protect newborns.

Research backed by the National Institutes of Health found pregnant moms who got vaccinated against COVID-19 generated antibodies against the virus, which “effectively crossed the placenta and were also found in the cord blood.” 

Some experts have also theorized that protection could also pass through breast milk to babies, though a recent study called into question whether babies could absorb the antibodies. 

Those scientists still found the vaccines appeared to work to transfer antibodies to the baby during pregnancy.

“Notably, the majority of infants born to women who received primary SARS-CoV-2 vaccine during pregnancy still had substantial transplacental antibodies five months after delivery,” they wrote.